Rodents, especially rats, are, and for a long time have been, a major problem in metropolitan areas. One of the main problems of rats is their common domestication and lack of extreme fear of humans and preference of foods used by humans. While rats are a great problem in rural areas, the existence of many rats with many humans in metropolitan areas greatly magnifies their dangers and destructiveness.
It has been estimated that in the United States alone rats cause between one-half and one billion dollars annually in terms of direct economic losses. Most of these losses are occasioned by the contamination of foodstuffs while the rats are feeding and the physical damage to other materials because of the rat propensity to gnaw.
Rats are a hazard to the life, physical and mental health and welfare of human beings.
Rat bites are quite common. In a city such as Washington, D.C., for example, several thousand rat bites may be encountered each year. Great damage or death may be caused to infants or invalids. Several diseases are associated with rats, the most common of which are rat-bite fever, leptospirosis, salmonellosis from foods contaminated with rat droppings, trichinosis spread to people from hogs which eat garbage containing droppings of infected rats, and rat parasite spread diseases such as murine typhus fever, plague and rickettsialpox. Other diseases which have been traced directly to rats are toxoplasmosis, listeriosis, and lymphocytic choriomeningitis.
Ridding areas of rodents has always been a recognized problem to which time and energy have been devoted.
All successful methods require the diligent cleaning of areas and maintaining areas in cleanly condition with foodstuffs and garbage stored appropriately to prevent infiltration by rats. Even an area which has been substantially cleared of rats may become reinfected in a short time if the basic precautions of cleanliness and proper storage facilities are not maintained.
One of the most effective ways of ridding an area of rats is by the use of poisons. Many poisons have been developed which have fair rat-killing power, but are dangerous to other animals and humans, and create problems of availability of antidotes for use in case of accidents.
All poisons are inherently dangerous and must be prepared, mixed, distributed and used carefully.
Poisons are not only dangerous when swallowed, but also the dust and fumes of many poisons may be extremely dangerous when inhaled or when contacting broken skin of handlers. Many poisons create a great danger of secondary poisoning, that is, animals may feed on the carcasses of poisoned animals and thus become poisoned themselves, and humans may also become poisoned by eating the meat of poisoned animals.
In addition to the inherent dangers involved in the use of ordinary poisons for rat extermination, the exorbitant costs of time and money make their use prohibitive. For example, when the common poisoning methods are employed, extreme precautions must be taken to insure against access to the poison by children and dogs and cats by giving public notice and keeping records of poisoned locations.
Another way of ridding an area of rats is by trapping. While trapping is successful in small installations, the use of existing traps is usually not successful for large scale applications.
Another method of controlling rats lies in the use of sound or ultrasonic radiation to keep rats out of protected premises. While that method denies certain areas to rats, it may not be effective in destroying large rat populations.
A discussion of control of domestic rats is found in the U.S. Department of Health, Education and Welfare Public Health Service Pamphlets available from the Consumer Protection and Environmental Health Service, Environmental Control Administration, Rockville, Maryland 20852. An example of such a publication is PHS Publication 563 (1956, 1969) entitled "Control of Domestic Rats and Mice".
A collection of descriptions of systems and apparatus for controlling rodents and vermin is found in the United States Patent Office Classification of Technology at Class 43, and particularly in subclasses 58 through 73. There are found United States patents officially classified within that class and cross-referenced into that class, unofficial references collected by the examiner, and foreign patents and publications collected by the examiner. Examples of disclosures found in that class are: U.S. Pat. Nos. 329,960; 710,020; 938,397; 1,020,690; 1,102,896; 1,108,724; 1,115,681; 1,139,587; 1,161,558; 1,163,071; 1,168,252; 1,314,200; 1,446,609; 1,538,308; 2,056,882; 2,255,955; 2,387,328; 2,962,836; 3,528,190 and Ser. No. 462,501.
Many problems remain in known existing systems and devices for the control of rats. Some of the problems are the inherent dangers of known chemicals used in poisoning techniques, the difficulties of trapping and killing rats in small numbers, and the lack of large scale apparatus for the systematic collection and destruction of rats without dangers of poisons and inefficiency of micro operations.